Changing coastal oceanography of the Black Sea II: Mediterranean effluent

This article describes the hydrography of the Northwestern Shelf (NWS), of the Black Sea emphasizing the changes induced by water management in the Dniejer and Dniester river basins. The existing literature and previously unpublished data have been reviewed and synthesized to describe water property fields and transport mechanisms of the NWS and the Dnieper and Dniester estuaries before the early 1960s, or the so-called precontrol period, when the effect of artificial river flow control upon the coastal waters was insignificant.After the hydroenergy complexes and water withdrawal and disposal systems on rivers became fully operational in the early 1970s (the so-called postcontrol period), the annual river discharge from the Dnieper and Dniester had noticeably decreased and seasonal river flow patterns had been artificially modified. Instead of a powerful and short early spring flood, typical for the natural conditions in the Dnieper river, the hydrographs in the postcontrol period exhibit two smaller peaks of river discharge of much longer period. One of them (winter-early spring) is caused by intense hydroenergy generation and weir discharges through the cascade of storage reservoirs. Another is associated with spring flood, modified by intense water consumption and storage in this period. High average river discharge in late May—early June strengthened the summer pycnocline which inhibits vertical mixing in the estuaries and coastal waters. Owing to a slow summer circulation, the rate of natural purification of the entire coastal system has been reduced. This coupled with the increased nutrient, organic and pollutant transport, decreased the dissolved-oxygen concentration and led to anoxic events and mass mortalities of marine organisms in the previously productive regions. These effects have primarily plagued the benthic communities along the entire western coast of the NWS since 1973.Winter convective overturn in the Black Sea reaches its maximum depth at the southern boundary of the NWS. Thus, the NWS waters descend beneath the seasonal and main thermoclines in the open sea and are spread by the prevailing currents across the entire sea in the cold intermediate layer (CIL). By this dynamic mechanism the projected man-made modifications in the riverine-estuarine systems of the NWS will affect and change the large-scale thermohaline structure and marine life of the Black Sea.     

Oxygen Uptake During Repeated Exposure to Temperature Change: Physiological Divergence in Panamanian Cognate Pairs and Latitudinally Distant Populations of Decapod Crustacea

Abstract. The emergence of the Isthmus of Panama subdivided the amphi-American biota. In the present study, Pacific and Atlantic populations of four cognate pairs of crabs were used to discern whether exposure to different thermal regimes in habitats, in the putative absence of gene flow, has resulted in physiological divergence. Populations that potentially form a common genetic pool were also used; these were populations of the Atlantic Panama cognate that occur in Belize and Florida. Decreases in water temperature occur periodically in Pacific Panama and Florida, but not in Atlantic Panama or Belize. In this study, physiological divergence in oxygen uptake was assessed in response to repeated exposure to either control and decreased temperature or control and increased temperature. Results indicate that, in only some of the genera tested, exposure to decreases in habitat temperature has resulted in divergence. Partial support is found for the corollary that adaptation to an environment with periods of decreased temperature results in reduced compensation during exposure to elevated temperature.     

Harmonic generation past a submerged porous step

Experiments were conducted in a wave flume to study the differences between harmonic evolution of monochromatic waves as they propagate over a submerged impermeable or porous step under non-breaking conditions. Results are used as a preliminary analysis to establish some engineering design criteria on harmonic generation on submerged porous structures. The root-mean-squared wave height evolution is also studied and compared to linear models as a first approximation. It is shown that porous structure increases the effective relative depth and decreases the relative wave height, resulting in a lower Ursell number and a lower chance to generate harmonics. The effective water depth over a step as defined in the paper, provides information to evaluate the potential harmonic generation.     

Data assimilation for a coastal area morphodynamic model: Morecambe Bay

This paper investigates the use of data assimilation in coastal area morphodynamic modelling using Morecambe Bay as a study site. A simple model of the bay has been enhanced with a data assimilation scheme to better predict large-scale changes in bathymetry observed in the bay over a 3-year period. The 2DH decoupled morphodynamic model developed for the work is described, as is the optimal interpolation scheme used to assimilate waterline observations into the model run. Each waterline was acquired from a SAR satellite image and is essentially a contour of the bathymetry at some level within the inter-tidal zone of the bay. For model parameters calibrated against validation observations, model performance is good, even without data assimilation. However the use of data assimilation successfully compensates for a particular failing of the model, and helps to keep the model bathymetry on track. It also improves the ability of the model to predict future bathymetry. Although the benefits of data assimilation are demonstrated using waterline observations, any observations of morphology could potentially be used. These results suggest that data assimilation should be considered for use in future coastal area morphodynamic models.     

A low level supplementary heating system for free divers

A simple and effective method of heating divers in extreme cold water has been developed. The local heating concept utilizes a uniformly distributed granular mixture of magnesium and iron particles packed in small sachets. Upon activation by sea water, the two metal mixture behaves as a multitude of short-circuited electrolytic cells, producing thermal energy rather than electrical energy. The 45 mm-square sachets may be placed where heating is required on the diver's body, thus giving rise to the term “local heating”, obviously, the heating system requires no pumping device, or distribution network. Heating rate and duration of output of the sachets are controlled by particle size, and mixture ratio of the constituent Mg and Fe particles.This paper described the development, testing and performance of the heating sachets. Results of live tests in different dive situations are also presented and discussed.     

Tank wall effects on broadside current forces on barge models

Three different barge sizes were tested in uniform current in a tank of limited width. One of the barges was tested with and without bilge keels. Tests were conducted in both deep and shallow water. The barges were placed broadside to the current flow and the lateral forces on the barges were measured. The effect of the tank walls on these forces is clearly shown.     

Resource decline and adaptation through time: Fishers in San Miguel Bay, Philippines, 1980–1993

This article examines social conditions in a bay experiencing population growth, gear conflict, overfishing, and general resource decline. Sample surveys of fishing households carried out in 1980 and 1993 in nine villages of San Miguel Bay reveal patterns of continuity and change. The key continuity is sustained overall population growth in fishing villages. Among the key forms of change are those which demonstrate a degree of adaptation to resource decline: decreased participation in fishing; greater reliance of fishing households on nonfishing income; increased dependence on remittances of nonhousehold children; increased participation of women in nonhousehold labor; and dramatic growth in the number of fishing organizations involved in resource management. The findings suggest that resource management policies should be patterned after spontaneous adaptations to resource decline.